What is the black/silver spot in Photron hollow cathode lamps?
A. The black/silver spot is what we call the getter. If you look closely at the centre of the black spot on the internal lamp structure you will see a ring. This ring is a barium getter. It has been activated by an RF generator; hence the black/silver spot. What does it do? The material on the inside wall acts as a trap, to catch impurites within the gas of the lamp. If a di-atomic particle hits this material, it becomes stuck to the wall. Therefore the getter keeps the gas clean throughout the life of the lamp.
